This invention relates to He-Ne double frequency lasers for generating a large. Adjustable frequency difference and relates to a short He-Ne laser for getting stabilized power output.
The Current double frequency laser are based on combination of Zeeman affect and mode pulling affect. The laser is comprising of an ordinary He-Ne laser and a magnet that produces a longitudinal magnetic field along the core of the laser tube. This kind of laser is not possible to obtain a large frequency difference. In general the frequency difference is only about a few MHz, however in many applications a large frequency difference, such as tens MHz even one thousand MHz, is needed.
In laser interferometers, a large frequency difference is used to enhance its measurement speed. For example the Optodyn Co. (USA) has been using tens MHz in its interferometers. The method generating larger frequency difference is to split a laser beam from an ordinary laser into two beams, then put an acoustic-optic modulator (acoustic-optic frequency shifter) or Brag cell in the way of one of the beams for change its frequency so that a large frequency difference rises between the two laser beam.
Large frequency difference is employed in Doppler Velocimeters. Such as Polytec Co. (West Germany). G. Bouchard (IBM J. RES. Develop. Vol. 29 No.3. 1985) and R. W. Whezien(Optical Engineering, Vol. 25, No.4. 1984).
At National Institute of Metrology of China (NIM), a special method has been using to get 1070 MHz frequency difference. The scientists design an appropriate length of the He-Ne laser to make the empty mode interval be 1070 MHz. Then an appropriate, strong, longitudunal magnetic field is applied on the He-Ne laser to make the spectrum of Ne atoms split into two spectrum lines and to coincide the central frequency of the two spectrum with the neighboring two empty mode.
The object of this invention is to design a new kind of He-Ne double frequency lasers without both magnets and acoustic-optic modulators in order to reduce the cost and simplify construction of double frequency laser, double frequency laser interferometers and Doppler velocimeters. This laser can obtain various frequency difference, form a few MHz to more than one thousand, to match different applications.
As additional but important result of this invention a short, tens mm. and power-stabled He-Ne laser can be produced. Short He-Ne lasers available in current market whose cavity length is shorter than 100 mm are of unstable power output.